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Monday, February 9, 2009

I just won another Where on (Google) Earth, this time WoGE #159 by Peter Luffi. It was an interesting structural area in northern California, showing the Franciscan Formation, the Great Valley sequence, and two major faults: the Stony Creek Fault and the Coast Range Thrust.

To win this WoGE #160, be the first to put the correct latitude and longitude in the comments, and describe the geology of the area! No Schott Rule this time, so have at it!!

3 comments:

46.335N-90.508W, Iron County, northern Wisconsin. The image features the western part of the SW-NE trending Gogebic Range, one of the various "iron ranges" belonging to the southern margin of the Superior Craton involved in the Paleoproterozoic (1.9-1.8 Ma) Penokean collision/orogeny. The southeastern third of the view is dominated by the Ramsey Formation consisting of Late Archean metabasalts. This is discordantly overlaid by deposits belonging to the Early Proterozoic Menominee Group and the Mid-Proterozoic Baraga Group, both parts of the Marquette Range Supergroup. Here the Menominee Group (the slightly prominent SW-NE diagonal ridge of the view) is represented by the Ironwood banded iron-formation (deposited in grabens of probably back-arc origin), which is economically important enough to inspire the name of a whole county :-) The overlying Baraga Group is represented by the Tyler Formation consisting of some black pyritic shales and local iron-formations near the base, followed by a massive turbiditic sequence. All these units are piled up in a fold and thrust belt formed during the Penokean collision between the Superior Craton and Pembine–Wausau terrane. They are covered (northwestern third of the view) by Mid-Proterozoic volcanic sequences defining the Powder Mill Group (basalts, andesites, lesser rhyolites of the Siemens Creek Volcanics and Kallander Creek Volcanics) and gabbroic rocks, all part of the continental rift-related Keweenawan Supergroup.

Alright Peter! And that's a lot more of the geology than I remembered, mostly just the Gogebic Range, not being mined too much anymore. A good place to find some "jaspilite" - which is what they sometimes call the hematitic version of the banded iron formations (BIFs), although I've never collected any in the Gogebic Range.